1. Technical Field
The present invention is related to the improved purification of flue gases containing sulfur dioxide by catalytic oxidation on moist activated carbon including a process of purification as well as a system for performing such a process.
2. Description of the Prior Art
Many processes are known to reduce the sulfur dioxide in exhaust gases or flue gases. Probably the most significant process to purify flue gases containing sulfur dioxide is by catalytic oxidation on moist activated carbon. One such process is disclosed in German Offenlegungsschrift No. 34 35 931. In this process, the flue gas laden with sulfur dioxide is first scrubbed in two steps with sulfuric acid which, on the one hand, saturates the flue gas with water vapor, and on the other hand cools the flue gas to the process temperature of the catalytic oxidation. The flue gas then passes over an activated carbon filter that is either continuously or intermittently sprayed with a sufficient amount of water so that a 3 to 20% sulfuric acid runoff is maintained. While the flue gas is passing through the activated carbon filter, the flue gas again becomes saturated with water vapor. Thereafter, clean gas exits the activated carbon filter and is sent into the atmosphere either directly or after a heating step.
Since this clean gas leaving the activated carbon filter is saturated with water vapor, a sufficient ascending force of the clean gas to rise through a guiding conduit, for example in a chimney, is not always guaranteed. To improve this ascending force, in another known process, the clean gas is either heated in an auxiliary device by hot flue gases (see, e.g., the magazine "STAUB" [Dust], Volume 47 (1987), page IV, figure ST 3769) or is indirectly warmed in one or more heat exchangers supplied with a separate energy source. Thus, the heated or warmed clean gas will rise better so as to reach the atmosphere, by way of a chimney, for example. However, use of the heat exchanger operating with a separate energy source is disadvantageous in that the use is accompanied by a considerable energy cost.